赣南东坑盆地早侏罗世侵入岩的锆石SHRIMP测年: 兼论赣南粤北地区成岩后期构造热事件

Besides the ages of the Early Jurassic Xialan complex in northern Guangdong Province, this paper reports the SHRIMP zircon U-Pb ages of magmatic rocks in Dongkeng and Linjiang basins, southern Jiangxi areas, southeastern China. The SHRIMP zircon U-Pb ages of 193 ±2Ma for granodiorite and 196 ± 1Ma for gabbro-diabase from Hanhu, Dongkeng basin, show that the mixed Hanhu complex intruded in the Early Jurassic, Field observation indicates that the gabbro-diabase coexists with syenite in granodiorite, and that the basic components enter the syenite. Another graniteporphyry pluton, about 8km east of Hanhu, is dated at 186 ±3Ma. In addition, the captured zircons of basalt from Linjiang basin yield SHRIMP U-Pb ages of 2570Ma, 1730Ma, 800Ma, 430Ma and 190Ma, showing that the basalt was formed later than 190Ma (the Early Jurassic). But the intruded Hanhu complex can't compose this basalt into a suit of bimodal volcanical rocks. These contemporary ages shed new light on the quiescent stage of magmatic activity in southern China during 200 - 180Ma, and revealed that the transition from the Tethyan to Pacific tectonic domains may have begun at or before ∼ 195Ma. Furthermore, the ⁴⁰Ar/³⁹ Ar ages of 132 - 137Ma for K-feldspar from both Hanhu and Xialan complexs suggest that there were no immediately later thermal events in southern Jiangxi and northern Guangdong areas until the Early Cretaceous. Owing to the subduction zone of the paleo-Pacific plate migrated oceanward to the southeast, the geodynamic system of southeastern China changed from compression to extension, and caused the production of voluminous Early Cretaceous igneous rocks. These rocks, in turn, influenced the Hanhu and Xialan complexs. The confirmation of these tectono-magmatic events will be helpful to understand the Early Jurassic tectonic evolution in this area.